Low passages of the P3HR-1 cell line, derived from nasopharyngeal carcinoma (NPC) and Burkitt's lymphoma (BL), were found to contain cell populations still capable of producing transforming virus, contrary to prior reports, which were stimulated through biological manipulation. These findings were supported by reactivity of monoclonal antibody directed against transforming EBV membrane glycoprotein, which stained cells propagated at 34 degree but not those propagated at 37 degrees C. Monoclonal antibody prepared against partially purified herpesvirus saimiri (HVS) was specific for HVS late antigen, failed to react with early and membrane antigen-producing cells, did not neutralize HVS, and did not react with either strain of herpesvirus ateles. IgA to EBV capsid antigen and antibody-dependent cellular cytotoxicity in NPC patients correlated with prognosis and treatment. Four anti-inflammatory agents and one protease produced variable effects on EBV early antigen expression; three of the anti-inflammatory agents inhibited early antigen induced by TPA, whereas no inhibition of early antigen induced by virus was seen, suggesting that TPA and virus induction of early antigen are mediated by different mechanisms.